1. Field of the Invention
This invention relates generally to the production of filamentary articles by melt extraction from a molten source. More specifically, the invention is directed to a method and apparatus for the production of continuous or discrete lengths of metal filaments by extracting the filaments from a molten bath of the metal with a rotating quench wheel.
2. Description of the Prior Art
The prior art is replete with systems by which continuous and noncontinuous lengths of filamentary articles are formed by melt extraction from a source of molten material through the use of a rotating quench wheel. This is basically achieved by contacting the surface of the bath with the peripheral chill edge or surface of the quench wheel which immediately removes heat from the molten material in contact therewith. This promotes solidification of the material upon the wheel, which solidified material is then continuously thrown from the periphery of the wheel by centrifugal force in the form of a discrete or continuous length filament.
The quench wheel utilized in such systems may assume various peripheral surface configurations, depending upon the desired configuration of the filamentary product. For example, the peripheral edge of the wheel may have a V-shaped configuration for producing wire or other filamentary articles having a small cross-sectional area. A quench wheel having a cylindrical shape will present a wide chill surface to the molten bath, thereby producing filamentary articles having flat configurations, such as ribbons or sheets. By providing the chill edge of the quench wheel with spaced notches or indentations, discrete filamentary articles having lengths equal to the peripheral distances between the notches may also be produced.
In addition to the shape of the periphery of the quench wheel, there are several other factors which serve to control the configuration of the filaments formed by the quench wheel in the practice of the melt extraction technique. These factors include the speed of rotation of the quench wheel, the temperature differential between the quench wheel and the molten bath, and the depth of immersion of the quench wheel chill surface into the bath. However, careful control of these operating parameters often do not provide the desired results, particularly in situations wherein it is desired to continuously extract a filament at high speeds from a molten bath of high melting point metal, such as steel.
The centrifugal motion of the quench wheel imparts a flinging action that serves to both remove the solidified filament from the wheel and also induce a whipping motion in the filament which sometimes causes breakage of the filament and prevents the formation of a continuous length thereof. Another problem inherent in melt extraction procedures is the formation of oxides and other undesirable reaction products in the area of the melt directly in contact with the quench wheel.
Still another problem encountered with melt extraction systems, and probably the most significant, is the inevitable fluid turbulence or bath instability which is created by the rotating quench wheel. This turbulence is directly proportional to the rotational velocity of the quench wheel and, at sufficiently high rotational velocities, causes the bath to form a surge wave which actually becomes free standing and moves away from the chill surface of the quench wheel. This undesirable situation naturally prevents the quench wheel from functioning in its intended chilling capacity and terminates the formation of the desired filament. As is therefore apparent, the rate of production of filamentary articles by the utilization of the quench wheel in the practice of the melt extraction technique is critically dependent upon the rotational velocity of the quench wheel. This velocity has heretofore been severely limited by the turbulence and other undesirable fluid dynamics realized in molten baths, particularly baths of molten metals.
The prior art has attempted to overcome the many problems, including bath instabilities, associated with the practice of melt extraction by adopting a variety of techniques and procedures. Melt extraction as presently known can broadly be classified into two basic categories.
The first category includes those systems utilizing an orifice for feeding molten material directly to the quench wheel. The early British Pat. No. 20,518 to Strange taught that metal strips or sheets may be produced by rotating the chill surface of a quench cylinder or disc against a meniscus of molten metal formed at the orifice of a molten metal supply channel. The metal is caused to be fed through the channel and come into contact with the quench surface at which point it is continuously formed into the solidified product and removed. This basic orifice technique is also disclosed by the more recent Bedell et al U.S. Pat. No. 3,863,700 wherein melt extraction of molten metal is achieved by elevating the melt through capillary action between two spaced solid members disposed in the melt. In this manner, an elevated concave meniscus is formed between the solid members for contact by the quench wheel. Bedell et al discloses that the use of this capillary action is advantageous in maintaining a constant height of melt for contact by the quench wheel and thereby stabilize the melt level against undesirable fluid dynamics such as turbulence or fluctuations in melt volume.
However, it has been recognized that the basic orifice technique is not without disadvantages, particularly when it is utilized with higher melting point molten metals. Under such circumstances, the materials making up the orifice can react with the higher temperature molten metal or the surrounding atmosphere, thereby degrading the properties and the dimensional integrity of the orifice material. The size and shape of the orifice thus tends to erode and provide products having nonuniform configurations. Moreover, the insoluble refractory materials making up the molten metal container or channel tend to erode and clog the orifice. The use of an orifice usually requires additional heating to insure that metal does not solidify in the relatively small opening. Further, the use of small orifices requires extremely clean melts to prevent intermittent plugging or restriction of the meniscus forming opening.
The second category of melt extraction systems comprise those which utilize a free or open bath of molten material. The rotating quench wheel is caused to contact or "kiss" the free open surface of the melt in the absence of any confining or constricting appliance other than the main container holding the melt. Examples of methods and apparatus utilizing the open bath concept are disclosed by the Stewart et al U.S. Pat. No. 3,812,901, Kavesh U.S. Pat. No. 3,856,074, Mobley et al U.S. Pat. No. 3,861,450 and Maringer et al U.S. Pat. No. 3,904,344. The use of an open bath for contact by the quench wheel presents an unrestricted environment for fluid turbulence resulting from the pumping action created by the rotation of the quench wheel in the melt. Accordingly, the rate of production of filaments by quench wheels operating in an open bath is limited to the corresponding quench wheel rotation velocities below that which would otherwise cause undue turbulence of the cresting melt wave away from the quench wheel.
The present invention provides an improved method and apparatus for the melt extraction of a filamentary article from a molten bath without the disadvantages of heretofore known melt extraction techniques.
It is an object of the invention to provide an improved melt extraction system forming filamentary articles at extremely high production rates.
It is another object of the invention to provide an improved melt extraction system which is capable of rapidly producing both continuous and discrete filamentary articles having a variety of cross-sectional configurations.
It is yet another object of the invention to provide an improved melt extraction method and apparatus for rapidly producing a filamentary article of uniform dimension, size and configuration.
It is yet still another object of the invention to provide an improved method and apparatus for melt extraction wherein the turbulence and other undesirable fluid dynamics of the melt bath are positively controlled to permit rapid production of filamentary articles through high quench wheel rotational velocities.